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What is the CIDR notation for an IP?

Question

My firewall doesn't allow safelisting based on FQDN, and it requires CIDR for IPv4 notation. How can I convert my dedicated IP to this format? 

 

Product

Twilio SendGrid (Email API and Marketing Campaigns)

 

Answer

  • For specific IPs, the CIDR notation should be IPv4/32. For example: 23.34.145.67/32

  • If you have a range of IPs where only the last octet differs, and you don't want to enter each IP separately, you can use the following notation: IPv4/24. 

    For example, 23.34.145.0/24 covers the range 23.34.145.0 to 23.34.145.255

  • If you have a range of IPs where the last two octets differ, and you don't want to enter each IP separately, you can use the following notation: IPv4/16. 

    For example, 23.34.0.0/16 covers the range 23.34.00 to 23.34.255.255

 

Additional Information 

Please note that SendGrid doesn't recommend the use of IP safelisting/pinning for other purposes, because we regularly turn on and off the IP addresses for maintenance or failures.

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